WO2016117732A1 - Handover method for mobile communication services - Google Patents

Abstract

The disclosed handover method for a mobile communication system comprising steps in which: a serving base station, which has determined a handover of a mobile communication terminal, selects multiple cooperative base stations; the serving base station makes a handover request to the selected cooperative base stations; the cooperative base stations respond to the serving base station with respect to the handover request; the cooperative base stations make a request for multicasting and receive packet data; the serving base station makes a request for RRC connection reconfiguration to the mobile communication terminal; while checking channel environments with the serving base station and cooperative base stations in real time, the mobile communication terminal makes a request for the packet data to the serving base station or the cooperative base stations and receives the packet data until a preset handover threshold condition is satisfied; and the mobile communication terminal performs the handover from the serving base station to any one target base station among the cooperative base stations if the handover threshold condition is satisfied.

Description

Handover Method for Mobile Communication Service

The present invention relates to a handover method for a mobile communication service, and more particularly, a handover method of a mobile communication terminal provided with a mobile communication service, a handover support method of a base station for the same, and a hand of the mobile communication system by the same. It's about the over way.

As is well known, 3GPP Release 8 describes an Evolved Packet Core (EPC), which is a network architecture, as one of mobile communication systems. EPC is a collection of network nodes for a 3GPP Long Term Evolution (LTE) system. EPC has evolved the core network of the existing 3GPP system architecture to support Evolved-UMTS Terrestrial Radio Access Network (E-UTRAN), which is an evolved RAN, and to improve the efficiency of packet networks. In order to simplify the network node, it has an efficient network structure. A wireless communication system including an EPC and an E-UTRAN may be referred to as an EPS (Evolved Packet System), and an LTE mobile communication system currently serving in Korea corresponds to this.

Meanwhile, in such a mobile communication system, handover is performed to provide a continuous service even while the mobile communication terminal is in motion. Such a handover can be largely divided into a hard handover and a soft handover.

Among these, the hard handover first disconnects from the serving base station during the handover process and performs the connection to the target base station. Soft handover, on the other hand, disconnects from the serving base station after the connection with the target base station is completed. Soft handover is superior to hard handover in terms of spectral efficiency or capacity because there is a section where both base stations are simultaneously connected during the handover process, but the radio link is twice as large as the hard handover. There are disadvantages to using more.

Semi-soft handover combines the advantages of hard and soft handover. In general, during the handover process, the distance between the serving base station and the target base station is similar, and the fading effects of the channels are added together, and the signal between both base stations undergoes a severe change with a similar average. Quasi-soft handover exploits this change opportunistically to achieve diversity gains by adaptively changing radio resources with better signal quality between the serving base station and the target base station. This is called a site selection diversity (SSDT).

Such semi-soft handover has an advantage of using the same amount of radio resources as the hard handover, while improving frequency efficiency compared to hard handover through the use of opportunistic signals.

In recent years, mobile communication systems are actively researching small cells in order to increase the capacity of a network. Accordingly, frequent handovers accompanying the miniaturization of the base station service area cause a decrease in the quality of service (QoS). There was a problem.

According to an embodiment of the present invention, high QoS is achieved by reducing handover by utilizing a plurality of cooperative base stations as well as a serving base station in adaptively changing radio resources having a better signal quality, such as a semi-soft handover. It improves the frequency efficiency at the same time.

The problem to be solved of the present invention is not limited to those mentioned above, and another problem to be solved which is not mentioned will be clearly understood by those skilled in the art from the following description.

The handover method of the mobile communication system according to the first aspect of the present invention comprises the steps of the serving base station that determines the handover of the mobile communication terminal to select a plurality of cooperative base stations, the handed to the cooperative base stations selected the serving base station Requesting over, the cooperative base stations responding to the serving base station in response to a handover request, the cooperative base stations requesting multicasting, receiving packet data, and the serving base station receiving the mobile communication terminal. Requesting an RRC (Radio Resource Control) connection reset to the mobile station, and checking the channel environment with the serving base station and the cooperating base stations in real time until the preset handover threshold condition is satisfied. Or requesting and receiving packet data from the cooperative base stations; The mobile communication terminal may include performing a handover from the serving base station to a target base station among the cooperative base stations when the handover threshold condition is satisfied.

Here, in the step of requesting and receiving the packet data, the serving base station and the cooperative base stations are multiple input multiple outputs (MIMOs) according to a comparison result of a channel environment with the mobile communication terminal and a preset transmission mode threshold. ) You can use any one of the transmission modes.

When any one of the plurality of MIMO transmission modes is selected and the packet data is transmitted, the mobile communication terminal may switch to a filter corresponding to the selected MIMO transmission mode to receive the packet data.

The serving base station and the cooperative base stations may use the spatial multiplexing transmission mode when the signal-to-interference and noise ratio (SINR) with the mobile communication terminal exceeds a preset transmission mode threshold.

In the method for supporting handover of a base station according to the second aspect of the present invention, when the handover of the mobile communication terminal is determined, selecting a plurality of cooperative base stations; and requesting handover from the selected cooperative base stations and receiving a response; Requesting the mobile communication terminal to reestablish an RRC connection; receiving packet data requested by the cooperative base stations to a mobility management node according to the handover request; and a channel environment with a serving base station and the cooperative base stations. And providing the packet data until the mobile communication terminal for real time checking satisfies a preset handover threshold condition, and wherein the handover threshold condition is satisfied, which one of the cooperative base stations is received from the serving base station. Recalling the mobile communication terminal that performed the handover to one target base station It may comprise the step of releasing the switch.

Here, in the step of providing the packet data when requested, the serving base station and the cooperative base stations are any one of a plurality of MIMO transmission modes according to a comparison result of a channel environment with the mobile communication terminal and a preset transmission mode threshold. Transmission mode is available.

The serving base station and the cooperative base stations may use the spatial multiplexing transmission mode when the SINR with the mobile communication terminal exceeds a preset transmission mode threshold.

A handover method of a mobile communication terminal according to a third aspect of the present invention comprises the steps of: receiving an RRC connection reconfiguration message for handover from a serving base station, a plurality of cooperative base stations and the serving base station included in the RRC connection reconfiguration message; Requesting and receiving packet data from the serving base station or the cooperating base stations until a predetermined handover threshold condition is satisfied while real-time checking a channel environment of the channel environment; and if the handover threshold condition is satisfied, the serving base station And performing a handover from the cooperative base stations to any one of the target base stations.

In the requesting and receiving of the packet data, the mobile communication terminal selects one transmission mode among a plurality of MIMO transmission modes by the serving base station and the cooperative base stations and transmits the packet data. The packet data may be received by switching to a filter corresponding to the MIMO transmission mode.

According to an embodiment of the present invention, high QoS is achieved by reducing handover by utilizing a plurality of cooperative base stations as well as a serving base station in adaptively changing radio resources having better signal quality, such as quasi-soft handover. It improves the frequency efficiency at the same time.

Furthermore, by using a suitable transmission mode among a plurality of MIMO according to the channel environment, there is an effect of further improving the frequency efficiency.

1A and 1B are flowcharts illustrating a handover method of a mobile communication system according to an exemplary embodiment of the present invention.

2 is a flowchart illustrating a handover support method of a base station according to an embodiment of the present invention.

3 is a flowchart illustrating a handover method of a mobile communication terminal according to an embodiment of the present invention.

4 is a graph showing simulation results for a handover method and a conventional handover method according to an embodiment of the present invention.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various different forms, and only the embodiments make the disclosure of the present invention complete, and the general knowledge in the art to which the present invention belongs. It is provided to fully inform the person having the scope of the invention, which is defined only by the scope of the claims.

In describing the embodiments of the present invention, if it is determined that a detailed description of a known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. In addition, terms to be described below are terms defined in consideration of functions in the embodiments of the present invention, which may vary according to intentions or customs of users and operators. Therefore, the definition should be made based on the contents throughout the specification.

1A and 1B are flowcharts illustrating a handover method of a mobile communication system according to an exemplary embodiment of the present invention.

As described above, the handover method of the mobile communication system according to the embodiment includes the steps 101 to 105 of the serving base station that determines the handover of the mobile communication terminal to select a plurality of cooperative base stations.

Subsequently, the serving base station further includes a step 107 of requesting handover to the selected cooperative base stations.

And further comprising steps 109 and 111 of the cooperating base stations in response to the handover request to the serving base station.

The method further includes steps 113 and 115 of the cooperative base station and the serving base station receiving packet data provided by the gateway by requesting multicasting from the mobility management node.

In addition, the serving base station further comprises a step 117 of requesting a radio resource control (RRC) connection reconfiguration to the mobile communication terminal.

Next, the mobile communication terminal checks the channel environment with the serving base station and the cooperative base stations in real time and requests and receives packet data from the serving base station or the cooperative base stations until the preset handover threshold condition is satisfied. 123).

If the handover threshold condition is satisfied, the mobile terminal further includes steps 125 to 129 of performing handover from the serving base station to one of the target base stations.

In addition, the mobile communication terminal further comprises the steps (131 to 137) of the other base stations releasing resources for the mobile communication terminal except for the base station attached through the handover.

Thereafter, the mobile communication terminal further includes a step 139 of receiving packet data provided by the gateway from the attached base station.

2 is a flowchart illustrating a handover support method of a base station according to an embodiment of the present invention.

As described above, the method for supporting a handover of a base station according to the embodiment includes selecting 201 a plurality of cooperative base stations when the handover of the mobile communication terminal is determined.

Subsequently, the method further includes a step 203 of requesting handover from the selected cooperative base stations and receiving a response.

The method further includes requesting the mobile communication terminal to reset the RRC connection (205).

Subsequently, the method further includes the step 207 of receiving packet data requested by the cooperating base stations to the mobility management node according to the handover request.

The method further includes a step 209 of providing a packet data request until the mobile communication terminal which checks the channel environment with the serving base station and the cooperating base stations in real time meets a preset handover threshold condition.

In addition, the method further includes a step 211 of releasing resources for the mobile communication terminal that has performed the handover from the serving base station to the target base station among the cooperating base stations because the handover threshold condition is satisfied.

3 is a flowchart illustrating a handover method of a mobile communication terminal according to an embodiment of the present invention.

As described above, the handover method of the mobile communication terminal according to the embodiment includes a step 301 of receiving a RRC connection reconfiguration message for handover from the serving base station.

Subsequently, requesting and receiving packet data from the serving base station or the cooperating base stations until the preset handover threshold condition is satisfied while real-time checking the channel environment with the plurality of cooperating base stations and the serving base station included in the RRC connection reconfiguration message. 303 is further included.

Next, if the handover threshold condition is satisfied, the method further includes the step 307 of performing a handover from the serving base station to any one of the target base stations.

Hereinafter, a handover method of a mobile communication terminal, a handover support method of a base station, and a handover method of the mobile communication system by the same according to an embodiment of the present invention will be described in detail with reference to FIGS. 1A and 1B to 4. Let's look at it.

First, the serving base station to which the mobile communication terminal is attached receives packet data for the mobile communication terminal from the gateway, and transmits the received packet data to the mobile communication terminal (101).

The mobile communication terminal receiving the mobile communication service through step 101 measures the radio wave environment for the base stations located in its vicinity including the serving base station and transmits a report on the measured radio wave environment to the serving base station. For example, the mobile communication terminal can measure and report a signal-to-interference and noise ratio (SINR) for radio waves transmitted from respective base stations (103).

Then, the serving base station determines whether the comparison result with the predetermined threshold value satisfies the handover evaluation index when there is a base station with better radio environment than the base station based on the radio environment report provided from the mobile communication terminal. If the evaluation index is satisfied, the handover of the mobile communication terminal is determined (105).

Subsequently, in step 105, the serving base station selects a plurality of base stations satisfying the handover evaluation index as the cooperative base station (201), and transmits a handover request message to the selected cooperative base stations (107).

And, when receiving the handover request message, the cooperative base stations identify the resources they have, and determine whether there is room for service, and performs admission control to allow handover when there is service space (109). The performed cooperative base stations transmit a handover request response message to the serving base station (111, 203).

In addition, the cooperative base stations that perform admission control in step 111 request multicasting from a mobility management entity (MME) to receive user data (113), and the mobility management node forwards the multicasting request to the gateway. The gateway transmits the packet data for the mobile communication terminal to the serving base station and the cooperative base stations in a multicasting manner (115).

Meanwhile, in step 111, the serving base station receiving the handover request response message from the cooperative base stations requests the mobile communication terminal to reset the RRC connection to the mobile communication terminal. At this time, the RRC connection reconfiguration request message includes information on the cooperative base stations that performed the admission control in step 109 (117, 205, 301).

Then, the mobile communication terminal attaches the cooperative base stations as the target base station according to the RRC connection reconfiguration request message (119), and requests and receives packet data from the target base stations including the serving base station and the cooperative base stations (121, 123). , 303). In view of the serving base station or the cooperating base station, the packet data received from the gateway is provided to the mobile communication terminal (207, 209).

Herein, the mobile communication terminal selects a base station having excellent propagation environment from the serving base station and the cooperative base stations while checking the channel environment with the serving base station and the cooperative base stations in real time, and requests packet data from the selected base station. Receive. The request and reception of such packet data are performed until the preset handover threshold condition is satisfied. For example, the preset handover threshold condition is a case where the SINR with one of the target base stations exceeds the preset handover threshold, and it is preferable to handover to the base station at this time.

In addition, the serving base station and the cooperative base station compares the channel environment with the base station and a preset transmission mode threshold value, and selects one transmission mode among a plurality of multiple input multiple output (MIMO) transmission modes according to the comparison result.

MIMO system has several transmission modes unlike SISO (Single Input Single Output) system. For example, MIMO transmission modes defined in the 3GPP standard include open loop spatial multiplexing (OL-SM), closed loop spatial multiplexing (CL-SM), beamforming (BF), and transmit diversity (TD). Each of these transmission modes exhibits different efficiencies depending on the channel environment. In general, the spatial multiplexing (SM) shows a high gain in a sufficiently guaranteed SINR, rich-scattering environment, and the BF and TD dominates the spatial multiplexing in a low SINR and low scattering environment. Has the performance.

Therefore, the target base stations adaptively switch these MIMO modes according to channel conditions according to SINR and channel rank with the mobile communication terminal. For example, the target base stations may use the spatial multiplexing transmission mode when the SINR exceeds a preset transmission mode threshold value, or may use an orthogonal space-time block code (OSTBC) transmission mode.

Herein, the mobile communication terminal switches to a filter corresponding to a transmission mode selected by the target base stations to receive packet data. For example, in the case of a spatial multiplexed transmission mode, packet data can be received by switching to a ZF (zero-forcing) filter or a minimum mean squared error (ZF) filter, and in the orthogonal space-time block code transmission mode, the maximum ratio Packet data may be received by switching to a Maximum Ratio Combining (MRC) filter.

Next, the mobile communication terminal determines the handover when the radio environment with one of the target base stations satisfies the preset handover condition (125, 305), and after the handover is determined, detaches the source base station . Here, the mobile communication terminal and the serving base station are detached so that the serving base station corresponds to the source base station (127, 307).

Subsequently, the mobile communication terminal transmits a handover confirmation message to the handed over base station (129). 1B illustrates a case where handover is performed to a cooperative base station #N according to an embodiment.

The cooperative base station #N transmits a handover complete message to the mobility management node (131), and transmits a packet rerouting message to the gateway (133).

In addition, the gateway transmits a resource release command to the other base stations except the base station to which the mobile communication terminal is attached through the handover (135), and thus the corresponding base stations release resources for the mobile communication terminal (137, 211). ).

Thereafter, the mobile communication terminal receives the packet data provided from the gateway from the attached base station (139).

Simulation was performed to verify the effect of the handover method of the mobile communication system according to an embodiment of the present invention, and the simulation environment is shown in Table 1 below.

Table 1 Cell radius 50 m Path loss exponent 3.68 Path loss constant 43.8 dB Shadowing standard deviation 8 dB BS Tx power 20 dBm Noise power density -166.83 dBm / Hz Channel bandwidth 10 MHz Number of cells 61 Frequency reuse factor One Tx antenna correlation 0.1

The result of this simulation is the graph of FIG. 4. In FIG. 4, the hard handover is the prior art, and the semisoft handover is the handover method according to the present invention. In both 2X2 MIMO and 2X4 MIMO, the handover method according to the embodiment of the present invention showed about 60% frequency efficiency improvement in the cell-edge region compared to the prior art.

Combinations of the steps of each flowchart attached to the present invention may be performed by computer program instructions. These computer program instructions may be mounted on a processor of a general purpose computer, special purpose computer, or other programmable data processing equipment such that the instructions performed through the processor of the computer or other programmable data processing equipment are described in each step of the flowchart. It will create a means to perform them. These computer program instructions may be stored in a computer usable or computer readable memory that can be directed to a computer or other programmable data processing equipment to implement functionality in a particular manner, and thus the computer usable or computer readable memory. It is also possible for the instructions stored therein to produce an article of manufacture containing instruction means for performing the functions described in each step of the flowchart. Computer program instructions may also be mounted on a computer or other programmable data processing equipment, such that a series of operating steps may be performed on the computer or other programmable data processing equipment to create a computer-implemented process to create a computer or other programmable data. Instructions for performing the processing equipment may also provide steps for executing the functions described in each step of the flowchart.

In addition, each step may represent a module, segment or portion of code that includes one or more executable instructions for executing a specified logical function (s). It should also be noted that in some alternative embodiments, the functions noted in the steps may occur out of order. For example, the two steps shown in succession may in fact be performed substantially simultaneously or the steps may sometimes be performed in the reverse order, depending on the function in question.

The above description is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains may make various modifications and changes without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be interpreted by the following claims, and all technical ideas falling within the scope of the present invention should be construed as being included in the scope of the present invention.

Claims (9)

Selecting a plurality of cooperative base stations by the serving base station having determined handover of the mobile communication terminal; Requesting handover from the serving base stations by the serving base station; The cooperating base stations responding to a handover request to the serving base station; Requesting multicasting from the cooperative base stations to receive packet data; Requesting, by the serving base station, resetting a radio resource control (RRC) connection to the mobile communication terminal; Requesting and receiving packet data from the serving base station or the cooperating base stations until the mobile communication terminal satisfies a preset handover threshold condition while real-time checking a channel environment with the serving base station and the cooperating base stations; , And performing a handover from the serving base station to a target base station among the cooperating base stations by the mobile communication terminal when the handover threshold condition is satisfied. The method of claim 1, In the step of requesting and receiving the packet data, the serving base station and the cooperative base stations transmit a plurality of multiple input multiple output (MIMO) according to a comparison result of a channel environment with the mobile communication terminal and a preset transmission mode threshold. A handover method of a mobile communication system using any one of modes. The method of claim 2, The mobile communication terminal receives the packet data by switching to a filter corresponding to the selected MIMO transmission mode when any one of the multiple input multiple output (MIMO) transmission modes is selected and the packet data is transmitted. A handover method of a mobile communication system. The method of claim 2, And the serving base station and the cooperative base stations use a spatial multiplexing transmission mode when a signal-to-interference and noise ratio (SINR) with the mobile communication terminal exceeds a preset transmission mode threshold. Selecting a plurality of cooperative base stations when the handover of the mobile communication terminal is determined; Requesting handover from the selected cooperative base stations and receiving a response; Requesting a reset of a radio resource control (RRC) connection to the mobile communication terminal; Receiving packet data requested by the cooperating base stations to a mobility management node according to the handover request; Providing the packet data when requesting the packet data until the mobile communication terminal which checks a channel environment with a serving base station and the cooperative base stations in real time meets a preset handover threshold condition; And releasing resources for the mobile communication terminal that has performed the handover from the serving base station to a target base station among the cooperating base stations when the handover threshold condition is satisfied. The method of claim 5, wherein In the providing of the packet data upon request, the serving base station and the cooperative base stations transmit a plurality of multiple input multiple output (MIMO) according to a comparison result of a channel environment with the mobile communication terminal and a preset transmission mode threshold. A method for supporting handover of a base station using any one of modes. The method of claim 6, And the serving base station and the cooperating base stations use a spatial multiplexed transmission mode when a signal-to-interference and noise ratio (SINR) with the mobile communication terminal exceeds a preset transmission mode threshold. Receiving a radio resource control (RRC) connection reestablishment message for handover from a serving base station; Requests and provides packet data to the serving base station or the cooperative base stations until a predetermined handover threshold condition is satisfied while real-time checking a channel environment with a plurality of cooperative base stations and the serving base station included in the RRC connection reconfiguration message. Receiving steps, And performing a handover from the serving base station to a target base station among the cooperating base stations when the handover threshold condition is satisfied. The method of claim 8, In the step of requesting and receiving the packet data, the mobile communication terminal selects one transmission mode among a plurality of multiple input multiple output (MIMO) transmission modes by the serving base station and the cooperative base stations to transmit the packet data. And switching to a filter corresponding to the selected MIMO transmission mode to receive the packet data.

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